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Assessing Biological Integrity of Surface Waters

United States
Environmental Protection
Office of Water
Office of Wetlands, Oceans
and Watersheds (4502-F)
July 1998

Wetland Bioassessment Fact Sheet 1

Biological Assessments Can Detect the Effects of the following Stressors

The objective of the Clean Water Act is to "maintain and restore the chemical, physical, and biological integrity of our Nation's waters." When the Clean Water Act was passed in 1972, the discharge of chemicals was commonly viewed as the primary threat to the health of our Nation's waterbodies. To track progress in reducing this threat, the Nation focused on developing chemical criteria which set numerical limits for safe levels of chemicals in waterbodies. During the past 25 years, the Nation has been largely successful in reducing the number and quantity of chemicals discharged into waterbodies by factories, wastewater treatment plants, and other point sources. During this same period of time, it has become increasingly clear that aquatic ecosystems are impacted by more than just chemicals. Aquatic ecosystems are altered by nonpoint source runoff, habitat alteration and fragmentation, introduced species, changes in the quantity and flow of water, and land use within a watershed. Traditional chemical criteria alone are unable to measure the impacts caused by these stressors. The EPA is now focusing on developing biological criteria in addition to chemical criteria to help track progress in maintaining and restoring the health of our waters. In most cases, the most direct and effective way to assess the "health" or biological condition of waterbodies is to: (1) directly measure the condition of their biological communities, and (2) support those data when necessary by measuring the physical and chemical condition of waterbodies and their watersheds.

Biological integrity is "the ability of an aquatic ecosystem to support and maintain a balanced, adaptive community of organisms having a species composition, diversity, and functional organization comparable to that of natural habitats within a region."
Karr, J. R. and D. R. Dudley. 1981. Ecological perspective on water qualitygoals. Environmental Management 5:55-68.

As human activities degrade the condition of a waterbody, the changes are reflected by the characteristics of the plant and animal assemblages living in the waterbody. Biological communities are sensitive to chemical, physical, and biological stressors and will reflect any changes to their environment. For example, the diversity of plant and animal assemblages will typically decrease when impacted by acidification. The composition of assemblages will also change as (1) species that are sensitive to acidic conditions decline in numbers and (2) species that can tolerate acidic conditions increase in abundance. For other stressors, such as nutrient enrichment, taxa richness may initially increase and then decrease. The challenge facing water quality agencies is to develop biological assessment methods to quickly and accurately evaluate the integrity of aquatic ecosystems.

Conducting a Biological Assessment

The process of conducting a biological assessment is similar to a doctor performing an annual physical on a human patient. A simplified three step process is described below.

1. Collect Supporting Information:

Collect background information and try to identify potential threats to the waterbody's condition. What type of wetland is it? Where is it located in its watershed? Was it ever drained or altered? What are the surrounding land uses that might influence it?

2. Perform Standard Tests and Measurements:

Directly measure biological attributes of the waterbody. Attributes that are good indicators of biological integrity are called metrics. The medical profession has already established a series of indicators, such as body temperature, to quickly assess the health of human patients. The challenge facing water quality agencies is to identify metrics that they can use to quickly assess the biological integrity of waterbodies (See Fact Sheet 5). During this screening process, conduct standard observations and measurements of the chemical and physical characteristics (e.g., temp, pH) of the wetland and its surrounding landscape. These data help a scientist accurately diagnose what is damaging the wetland and to prescribe remedies.

3. Compare to Reference Conditions:

When a doctor takes a patients pulse or temperature, she compares the readings to the conditions of healthy people. The doctor uses the measurements from the healthy people as reference conditions. Similarly, a scientist compares the environmental conditions of a waterbody to minimally-impacted reference sites of the same type and region of the country. The reference sites provide a range of biological and environmental conditions that should be expected in that type of waterbody and region in the absence of human disturbances.

After comparing the measurements to the reference conditions, the scientist may give the waterbody a clean bill of health or may spot a warning sign. If the scientist spots a measurement that falls outside of the normal range, then the the scientist may decide to take more detailed biological measurements to determine if there really is a problem. At this point the scientist may also conduct more complex chemical and physical tests to help diagnose the source(s) of the impairment. The background information and supporting chemical and physical data will help the doctor identify stressors and potential risks to the wetland.

Using the Framework of a Patient's Annual Physical to Compare Biological and Chemical Assessments

How a Patient's Annual Physical Would Proceed Using the Framework of a Biological Assessment

A patient schedules an appointment with a doctor for an annual physical. The doctor starts the physical by collecting background information by asking a series of questions to identify any risks to the patient's health. The doctor then performs a series of standard tests (pulse rate, blood pressure, etc.) that are indicators of the patient's health. The doctor compares the measurements to reference conditions of healthy people. If the doctor spots any warning signs or conflicting signals during this screening process, the doctor will ask more questions and perform more advanced (and expensive) tests to determine if the problem really exists and to help identify what is causing the problem.

How a Patient's Annual Physical Would Proceed Using the Framework of a Chemical Assessment

A doctor visits a patient's house to assess the environmental conditions in the house. The doctor measures the amount of chemicals in air and on the floor, tables, and other surfaces. If the doctor finds a lot of toxic chemicals in the house, such as mercury, then the doctor could say that there is a high probability that the patient is not completely healthy, even without directly examining the patient. But if the doctor does not find a lot of chemicals, then the doctor could reach an erroneous conclusion by relying only on the chemical data. By extrapolating from chemical exposure to the patient's health, the doctor could overlook many other factors that can influence the patient's health. The patient may be unhealthy even though there are no chemicals in the house. The patient may be exposed to chemicals outside of the home or chemicals for which the doctor did not conduct tests. The patient could be affected the combination of many different chemicals. More importantly, the patient could be harmed by a variety of physical and biological stressors, which are overlooked by standard chemical tests. The only way to know for sure if the patient is ill, is to directly examine the patient. By combining the chemical data with direct measurements of the patient's condition, the doctor can make a more accurate assessment of the patient's health and can then determine the most appropriate course of action.

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